In the case that a semiconductor integrated circuit is formed by use of a silicon photonics technique, a buried oxide (BOX) layer is formed on a silicon (Si) substrate, and an optical circuit comprising an optical element, an optical waveguide, and so on is formed as an SOI (Silicon on Insulator) layer (Si layer) on the BOX layer.
In the case that a semiconductor integrated circuit such as that explained above is used in a transmitter and/or a receiver of an optical communication system, an electrical signal wiring is formed on an SOI substrate. FIG. 1 shows a cross-section view of a prior-art semiconductor integrated circuit 100. A BOX layer 104 is formed on an Si substrate 102, an SOI layer 106 comprising an optical circuit is formed on the BOX layer 104, and an SiO2 layer 108 is formed on the SOI layer 106. Further, an electrical signal wiring 110 comprising aluminum (Al) or the like is formed on the SiO2 layer 108.
FIG. 2 shows a cross-section view of another prior-art semiconductor integrated circuit 200. A BOX layer 204 is formed on an Si substrate 202, an SOI layer 206 comprising an optical circuit is formed on the BOX layer 204, and an SiO2 layer 208 is formed on the SOI layer 206. A first electrical signal wiring 210 and an SiO2 layer 212 are formed on the SiO2 layer 208, and a second electrical signal wiring 214 is formed on the SiO2 layer 212.
In the semiconductor integrated circuits shown in FIGS. 1 and 2, the insertion loss in each of the electrical signal wirings 110, 210, and 214 is large.